It is well known that a radio signal arriving at a receiving antenna location can be scattered by objects in the environment, resulting in a signal at the receiver that is a combination of signals reflected or transmitted by the objects, diffracted by the objects, and/or attenuated through the objects. Such environments are called electromagnetic scattering environments. Conventional radio signal receivers sometimes employ antenna diversity to improve the received signal quality of such scattered signals, typically employing two antennas having different polarizations or two antennas separated, for example, by a wavelength of the carrier frequency. Different methods are used to combine the signals intercepted by the two antennas. A low cost method of switching between them can provide substantial improvement in some situations. A higher cost method of combining the signals that uses a radio frequency combiner will typically provide equal or better results. In conventional diversity antenna systems, a separation between two antennas is typically chosen to minimize the correlation of the signals being received at each antenna. Some cellular systems employ two antenna diversity systems for fixed equipment, in which a separation of two antennas that is determined by the carrier wavelength provide improved performance. Another example of separation diversity is found in wireless routers that operate according to the 802.11 (b) standard promulgated by the Institute of Electrical and Electronic Engineers (IEEE). In some of these systems, the fixed router unit has two antennas at fixed distances, but the antennas can be rotated, thereby changing their relative polarization. Polarization diversity can be obtained by using dual polarized antennas, which can require less enclosed volume and has provided improved performance in portable radios. Such approaches utilize fixed physical arrangements that are chosen to provide good improvement over non-diversity antennas in many situations. However, as the carrier frequencies that are used for new radio communication systems increase, the scattering of electromagnetic energy by objects in the environment has a more degrading impact on the received radio signal and the electromagnetic scattering environment can differ substantially between fixed locations that are not far apart. In these situations, the improvements afforded by a fixed physical arrangement of two diversity antennas diminished, and a better approach is needed.
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